Projector based on tunable individually-addressable Fabry-Perot filters

ABSTRACT

A projection system includes a display apparatus comprising a plurality of tunable Fabry-Perot filters, each of the filters being configured for shifting between a state in which the filter transmits radiation in a bandwidth in the visible range of the electromagnetic spectrum and a state in which the filter transmits radiation in a bandwidth outside the visible range of the electromagnetic spectrum. An illuminator provides light to the plurality of Fabry-Perot filters. A control system receives image data and controls the display apparatus to project an image onto an associated display surface. The control system includes a modulator which provides wavelength modulation signals to the plurality of Fabry-Perot filters to modulate a color of pixels in the image and causes selected ones of the Fabry-Perot filters to shift into the bandwidth outside the visible range to modulate the brightness of pixels in the image.

CROSS REFERENCE TO RELATED APPLICATIONS

Cross-reference is made to the following co-pending, commonly assignedapplications, which are incorporated in their entireties, by reference:

U.S. application Ser. No. 11/092,635, filed Mar. 30, 2005, entitled“TWO-DIMENSIONAL SPECTRAL CAMERAS AND METHODS FOR CAPTURING SPECTRALINFORMATION USING TWO-DIMENSIONAL SPECTRAL CAMERAS,” by Mestha et al.;

U.S. application Ser. No. 11/319,395, filed Dec. 29, 2005, entitled“SYSTEMS AND METHODS OF DEVICE INDEPENDENT DISPLAY USING TUNABLEINDIVIDUALLY-ADDRESSABLE FABRY-PEROT MEMBRANES,” by Mestha et al.;

U.S. application Ser. No. 11/319,389, filed Dec. 29, 2005, entitled“RECONFIGURABLE MEMS FABRY-PEROT TUNABLE MATRIX FILTER SYSTEMS ANDMETHODS,” by Wang, et al.;

U.S. application Ser. No. 11/319,276 filed Dec. 29, 2005, entitled“FABRY-PEROT TUNABLE FILTER SYSTEMS AND METHODS,” by Lin, et al;

U.S. application Ser. No. 11/016,952 filed Dec. 20, 2004, entitled “FULLWIDTH ARRAY MECHANICALLY TUNABLE SPECTROPHOTOMETER,” by Mestha, et al;

U.S. application Ser. No. 11/092,835, filed Mar. 30,2005, entitled“DISTRIBUTED BRAGG REFLECTOR SYSTEMS AND METHODS,” by Wang, et al.;

U.S. application Ser. No. 10/833,231, filed Apr. 27, 2004, entitled“FULL WIDTH ARRAY SCANNING SPECTROPHOTOMETER,” by Mestha, et al.; and,

U.S. application Ser. No. 10/758,096, filed Jan. 16, 2004, entitled“REFERENCE DATABASE AND METHOD FOR DETERMINING SPECTRA USINGMEASUREMENTS FROM AN LED COLOR SENSOR, AND METHOD OF PARTITIONING AREFERENCE DATABASE,” by Mestha, et al.

U.S. application Ser. No. 11/406,030, filed contemporaneously herewith,entitled “FABRY-PEROT TUNABLE FILTER,” by Lin et al.

BACKGROUND

The exemplary embodiment relates to micro-electromechanical systems. Itfinds particular application in connection with a projection devicecomprising an array of independently addressable Fabry-Perot membranesand will be described with particular reference thereto.

Flat panel displays, such as liquid crystal displays (LCD) are widelyused in a variety of applications, including watches, cell phones, andtelevision displays. These displays rely on the combination of light ofthree primary colors to achieve a range of colors. The range andintensities of the colors which can be achieved with LCDs are oftenlimited. The challenge is still in displaying rich chromatic colors athigh resolution and at low power consumption.

Projection systems have the advantage that they are unobtrusive whenturned off, since they can be smaller than a paperback book and can bemounted out of the way, on a ceiling or wall. Their size also makes themvery portable. LCD and micro-electromechanical (MEMS)-based projectorsare commonly used for business and home theater projection systems. Inan LCD projector, light is sent through a layer of liquid crystals thateither block or pass light by changing their polarization in response toan applied voltage. The color comes from red, green, or blue colorfilters placed in a grid that correspond to each of the three subpixelsthat make up a full pixel. MEMS-based projectors typically use an arrayof mirrors to reflect light onto the screen or shunt it away, with thecolor coming from a spinning color wheel that the light passes through,using the timing of the mirror movements to determine how much of eachcolor will be shown on the screen. To create high definition images, alarge number of mirrors are required to be individually operable,typically of the order of about a half to one million mirrors. The useof the color wheel limits the saturation of any one color, since itsmaximum duty cycle can only be 33% (assuming three colors). The colorgamut of these two methods is limited to colors inside the triangle inthe chromaticity diagram defined by the three filters. Thus theprojectors cannot display colors of higher chroma than that of theirfilters, which excludes about half of the colors that the human eye cansee. Additionally, since both systems require combinations of RGB(geographically separated or rapidly cycled in time) to create differentcolors within the visible range, the range of colors is limited.

INCORPORATION BY REFERENCE

The following references, the disclosures of which are incorporated byreference, are mentioned:

U.S. Pat. No. 6,295,130 to Sun, et al., issued Sep. 25, 2001, disclosesa Fabry-Perot cavity spectrophotometer.

U.S. Pat. No. 6,980,346 to Greer, et al. discloses a display devicewhich employs a Fabry-Perot filter having a tunable optical property.

US Published Application No. 20050226553, published Oct. 13, 2005,entitled “OPTICAL FILTRATION DEVICE,” by Hugon, et al., discloseswavelength selective optical components for transmitting light in anarrow spectral band, which is centered around a wavelength, and forreflecting the wavelengths lying outside this band. The componentincludes an input guide conducting light radiation to a tunable filter,and means for returning a first part of the radiation reflected by thefilter during the first pass in order to perform a second pass throughit.

BRIEF DESCRIPTION

Aspects of the exemplary embodiment relate to a projection system and toa method.

In one aspect, the projection system includes a display apparatuscomprising a plurality of tunable Fabry-Perot filters, each of thefilters being configured for shifting between a state in which thefilter transmits radiation in a bandwidth in the visible range of theelectromagnetic spectrum and a state in which the filter transmitsradiation in a bandwidth outside the visible range of theelectromagnetic spectrum. An illuminator provides light to the pluralityof Fabry-Perot filters. A control system receives image data andcontrols the display apparatus to project an image onto an associateddisplay surface. The control system includes a modulator which provideswavelength modulation signals to the plurality of Fabry-Perot filters tomodulate a color of pixels in the image and causes selected ones of theFabry-Perot filters to shift into the bandwidth outside the visiblerange to modulate the brightness of pixels in the image.

In another aspect, a method of projecting an image includes receivingimage data for an image to be projected and illuminating a plurality oftunable Fabry-Perot filters. Each of the filters is configured forshifting between a state in which the filter transmits radiation in abandwidth in the visible range of the electromagnetic spectrum and astate in which the filter transmits radiation in a bandwidth outside thevisible range of the electromagnetic spectrum. The method furtherincludes controlling the tunable Fabry-Perot filters to project theimage onto an associated display surface including providing wavelengthmodulation signals to the plurality of Fabry-Perot filters to modulate acolor of pixels in the image and causing selected ones of theFabry-Perot filters to shift into the bandwidth outside the visiblerange to modulate the brightness of pixels in the image in accordancewith the image data.

In another aspect, a projection system includes an image source whichsupplies image data for an image to be projected and an array ofindividually tunable Fabry-Perot filters mounted on a common transparentsubstrate, each of the filters being configured for transmitting visiblelight therethrough. An illuminator provides light to the plurality ofFabry-Perot filters. A control system receives image data and controlsthe display apparatus to project an image onto an associated displaysurface. The control system includes a modulator which provideswavelength modulation signals to the plurality of Fabry-Perot filters tomodulate a color of pixels in the image. A lens system includes an arrayof microlenses intermediate the array of filters and the associateddisplay surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a projection system according to theexemplary embodiment;

FIG. 2 is a side sectional view of an exemplary Fabry-Perot filteraccording to a first exemplary embodiment;

FIG. 3 is a top plan view of the exemplary Fabry-Perot filter;

FIG. 4 is a top plan view of a Fabry-Perot array according to a firstexemplary embodiment;

FIG. 5 is a top plan view of a Fabry-Perot array according to a secondexemplary embodiment;

FIG. 6 is an enlarged top plan view of the array of FIG. 4;

FIG. 7 is a side sectional view of the array of FIG. 6;

FIG. 8 is an enlarged side view of the display system of FIG. 1; and,

FIG. 9 illustrates steps of an exemplary method of projecting an image.

DETAILED DESCRIPTION

The exemplary embodiment relates to a display system and in particularto a projection display system, such as a television projection system,and to a method of displaying electronically stored information.

The display system may include a Fabry-Perot array and an illuminator.Each cavity of the array may be tuned to transmit colors ofcolor-separated incoming image pixels. For each color-separated imagepixel, multiple gray (brightness) levels may be achieved throughtime-division multiplexing of the transmitted light. In variousexemplary systems and methods, the display system may be atwo-dimensional flat panel matrix display system, with each individualpixel of the image having a color corresponding to the size of arespective cavity, with gray levels achieved using the time-divisionmultiplexing of the cavity. In other embodiments, image pixels may begenerated by the combination of outputs of a plurality of the cavitiestransmitting at the same wavelength band or at different wavelengthbands. The size and time-division multiplexing of the cavities provide adevice-independent display of the image with rich chromatic colors.

The exemplary embodiment includes a densely-packed,individually-addressable 2-dimensional array of Fabry-Perot cells(filters) with cavities which provide tunable gaps actuated byapplication of a voltage. As the gap changes, the reflections off theupper and lower surfaces of the Fabry-Perot cavity interfere, and theresulting wavelength of the transmitted light is that which producesconstructive interference. The ability to change the filter wavelengthband with time enables the filter to achieve a wider range ofwavelengths than can be achieved with other projection and flat panelsystems. The range of colors is dependent on the resolution of theFabry-Perot filter, which may be from about 5 to 100 nm, e.g., less than50 nm, and in one embodiment, about 10 nm. Each filter may thus haveabout thirty-one states in the visible region (about 400-700 nm)corresponding to thirty one wavelength bands with a peak wavelength ineach band. In one embodiment, colors may be created by combining theoutputs of two or more Fabry-Perot filters such that two or threewavelength bands are mixed together. For example, by combining threefilters, each with offset wavelength peaks, a wide range of colors canbe rendered. In one embodiment, some of the colors may be created byrapidly shifting the filter between two (or more) states at sufficientspeed that the two colors are indistinguishable to the eye and areviewed as a single combined color.

With reference to FIG. 1, an exemplary projection system includes adisplay apparatus 10, an image source 12, a control system 14 whichcomprises a modulator 15, an illuminator 16, such as a light source, anda display surface 18.

The display surface 18 can be a screen, such as a movie screen placed ona wall, or a screen forming a portion of a rear-projection televisionset, a wall or other surface from which the image can be viewed at adistance by a viewer's eye 19. In one embodiment, the display surface isa reflective surface, i.e., it reflects more light than it transmits.The display surface may be remote from the display apparatus 10, suchthat the image emitted by the display is enlarged multiple times beforereaching the display surface, such as at least 5 times, and in someembodiments at least ten times or at least 50 times.

The display apparatus 10 includes a two-dimensional array 20 of tunableFabry-Perot filters 22 which may be addressable individually oraddressable as small groups of Fabry-Perot filters. Light from thesource is focused on the display apparatus by a first optical system 24,such as a converging lens, which may generate a collimated beam of lightfor illuminating the array. A second optical system 26, intermediate thearray and the display surface 18, may include one or more projectionlenses. In the illustrated embodiment, the second optical system 26comprises a projection (diverging) lens 27 which includes and aconverging lens 28 spaced therefrom, both of which comprise a pluralityof adjoining microlenses 29.

The image source 12 may be any suitable source of digital images, suchas color images, and can include, for example, one or more of a digitalvideo disk (DVD) player, a wireless television tuner (e.g., receivinglocal or satellite signals), a cable television tuner (e.g., making useof electrical or optical signal reception), and a wireless computingdevice (e.g., a laptop computer, a personal digital assistant (PDA), anda tablet computer), among others.

The light source 16 may comprise one or more white light sources, suchas one or more of halogen lamps, fluorescent lamps, high intensity LEDs,and other high intensity sources capable of generating light inwavelengths throughout the visible range of the spectrum when energized.The range of colors which can be achieved is dependent, to some degree,on the light source, since if the source has gaps in its spectrum, theprojector will not be able to display that wavelength, regardless of thefilter's characteristics. If the strength of the illumination variesover the spectrum (as does sunlight), this could be accommodated byaltering the amount of time that the filter dwells in each state,spending longer at the colors that have less representation in theillumination.

The microlenses 29 of the second focusing device 26 may be created usinga mold. Alternatively, a polymer, e.g., an epoxy resin, such as SU8 (aphoto-imagable epoxy based on a fully epoxidized,bisphenol-A/formaldehyde novolac co-polymer, available from ShellChemical) could be patterned and then reflowed to create the desiredshape. Or, a self focusing (SELFOC) lens array could be used. Suchlenses are available, for example, from NSG America. Inc., Somerset N.J.08873.

The basic structure of each Fabry-Perot cavity or filter 22 comprisingthe array 20 may be as described, for example, in U.S. Pat. No.6,295,130, and co-pending application Ser. No. 11/092,635, which areincorporated herein by reference in their entireties. In general, theFabry-Perot filter includes two micro-mirrors separated by a gap. Thegap may be an air gap, or may be filled with liquid or other material.The micro-mirrors may be defined by membranes which are primarilysilicon (thin enough to avoid absorbing much light) or silicon nitrideand are optionally coated with multi-layered distributed Bragg Reflector(DBR) stacks or highly reflective metallic layers, such as gold. Avoltage applied between the two mirrors may be adjusted to change thedistance between the two mirrors. The space between the two mirrors isalso referred to as the size of the gap. Only incident light with acertain wavelength band may be able to pass the gap due to aninterference effect which is created inside the gap due to multiplereflections. Depending on the gap distance, it is possible to block thevisible light completely or transmit close to the maximum. Any heatdissipation resulting from blockage of all the light may be removed fromthe device using fans or other air circulating systems.

The control system 14 addresses the Fabry-Perot filters individually orin small clusters to achieve a selected wavelength band of each pixel inthe image and a selected gray level or intensity. The illustratedcontrol system includes a modulator 15 comprising an image datamodulator 30, a wavelength modulator 32, and a brightness modulator 34which may be individual components or combined into a single modulationcomponent. In addition to the modulator 15, the control system 14 mayfurther include a memory 36, an interface device 38, and a controller40, all interconnected by a connection or data bus 42, and as will bedescribed in greater detail below.

For example, FIG. 2 shows a side view of a portion of the array 20 whichincludes one embodiment of a micro-electro-mechanically tunable devicehaving a Fabry-Perot (F-P) micro-electro-mechanically tunableFabry-Perot filter 100 which will be referred to herein as aninterferometer or Fabry-Perot filter. FIG. 3 is a top view of theFabry-Perot filter 100. As shown in FIG. 2, the Fabry-Perot filter 100may include a first mirror 110 and a second mirror 112. In variousexemplary embodiments, the second mirror 112 may include a distributedBragg reflector (DBR) mirror that includes three pairs of quarterwavelength Si/SiN_(x) stacks. The first mirror 110 may include adistributed Bragg reflector (DBR) mirror that includes two pairs ofquarter wavelength Si/SiN_(x) stacks. SiN_(x) may be Si₃N₄. In anotherembodiment, one or both of the mirrors may be primarily Si. The additionof the DBR leads to a sharper spectral spike at the desired wavelength,increasing the spectral resolution.

In general, a driving method of a wavelength tunable optical filter canlargely be classified into two categories. One is to adjust a distancebetween mirrors by a force applied to the mirrors and to provide arestoration force by a structure connected to the mirror as in anelectrostatic scheme and the other is by a deformation of the drivingbody that is connected to the mirror as in a thermal expansion scheme,an electromagnetic scheme, or an external mechanical force scheme.

As shown in FIG. 2, the Fabry-Perot filter 100 may also include firstand second electrodes 114, 116. The first electrode 114 may be formed onthe first mirror 110 via a support element 118. The second electrode 116may be sandwiched between the second mirror 112 and a substrate 120.

The substrate 120 may have a portion 122 that may be a hole or atransparent part. The support element 118 and first and secondelectrodes 114,116 may be transparent. Indium tin oxide (ITO) may beused for forming the transparent electrodes 114,116.

The first and second mirrors 110 and 112 may be separated by a cavity130 to define a gap of distance 132 therebetween. The distance 132represents a dimension of the cavity 130, and may be referred to as asize or height of the cavity 130.

The first and second mirrors 110 and 112 are maintained in spaced apartrelation by flexible members, such as a plurality of springs 134, eachassociated with a respective anchor 136. The springs 134 are connectedat a first end to the support element 118 and at a second end to thefirst mirror 110 such that the first mirror 110 is spaced from thesecond mirror 112 to define the cavity 130, while permitting movementrelative to the second mirror.

The gap dimension 132 is changed or otherwise adjusted between minimumand maximum amounts to adjust the wavelength of light transmittedthrough the Fabry-Perot filter. For example, first mirror 110 may bedeformed to a dimensional change in the cavity 130 by applying a voltagein the range of 5-100 volts across transparent bottom electrode 116 andtransparent top electrode 114, or a charge in the range of 10⁻¹¹coulombs on transparent bottom electrode 116 and transparent topelectrode 114 to effect a change in the size 132 of cavity 130 of about300 to 500 nm. Hence, electrodes 114 and 116 may form a capacitor andthe Fabry-Perot Fabry-Perot filter 100 may have an associatedcapacitance. As the size 132 of cavity 130 decreases, for example, theFabry-Perot transmission peak shifts to shorter wavelengths.

The size 132 may be changed in a variety of ways. For example, the size132 may be changed in a way in which the first mirror 110 staysstationary, while the second mirror 112 moves relative to the firstmirror 110. Alternatively, the size 132 may be changed in a way in whichthe second mirror 112 stays stationary, while the first mirror 110 movesrelative to the second mirror 112. Alternatively, the size 132 may bechanged in a way in which both the first mirror 110 and the secondmirror 112 are moving relative to each other. In various exemplaryembodiments, the first mirror 110 and the second mirror 112 maintainparallel with each other regardless of the relative movement therebetween.

Furthermore, the size of the cavity 130 may be changed by a mechanismother than application of a voltage. For example, the size of cavity 130may be changed by a mechanical, thermal or magnetic mechanism.

In the Fabry-Perot filter 100 shown in FIG. 2, light may be received atthe top of the Fabry-Perot filter 100 through the top electrode 114. Thereceived light may be transmitted through the cavity 130 and the portion122 of the substrate 120 at a tuned wavelength.

The display apparatus 10 may be constructed to avoid or minimize deadspaces between the projected image pixels which result from the spacingbetween filters 22. One way of achieving this is by situating theFabry-Perot filters 22 close together with little space between them.FIGS. 4 and 5 show two designs suitable for projection systems. As shownin FIG. 4, the array 20 may include a plurality of adjacently locatedFabry-Perot filters 22. For clarity, only the support elements 118,springs 134, and anchors 136 are illustrated in this figure. The mirrorsand electrodes are not shown. Although FIG. 4 shows a 5×5 array ofcavities 130, it will be appreciated that in practice the array may bemuch larger and may include at least 600 devices per linear inch (dpi)as an N×M array, where N and M are integers. In some embodiments, thefilters 22 may be less than 50 μm in both dimensions of the plane, e.g.,20-25 μm, corresponding to about 1000-1200 dpi.

In FIG. 4, thin silicon membranes (not shown) which define the firstmirrors 110 are attached directly to the silicon springs 134 that allowthem to move. The silicon membranes are thin enough to be transparenteven at the lower visible wavelengths. In the embodiment of FIG. 5,nitride membranes (not shown) are attached to the silicon frame 118 atthe corners. Spaces between the membranes are indicated at 160. Anenlarged view of the silicon membrane version of FIG. 4 is shown in FIG.6 and in cross section in FIG. 7, where Distributed Bragg Reflectors162, 163 of mirrors 110, 112 are illustrated. Reflector 162 is supportedon a silicon membrane 164.

The illustrated membrane 164 supports top electrode 114 on its uppersurface. Alternatively, the membrane may act as the top electrode. Whilethis has certain advantages in that the two plates of the electrodes arecloser together, making the electrostatic attraction stronger, there areadvantages in placing the electrode on top of the electrode. Since themirror layers are very thin, having the membrane act as the secondelectrode tends to make the electrostatic gap be nearly the same as theoptical gap. When an electrostatic device is actuated and the gapbetween the plates closes to about two thirds of its original value, theelectrostatic force overcomes the biasing effect of the springs andcauses the plates to snap together. This motion is not controllable, andthus limits the controllable motion to about one third of the totalelectrostatic gap. Since it is desirable for the optical gap to have arange of from about 350 nm to 200 nm, which is a decrease of more thanhalf, the actuation may not be controllable over this range if themembrane serves as the electrode. By putting the electrode on top, theelectrostatic gap is larger than the optical gap, and one third of thatlarger gap provides the desired range of motion for the optical gap.

The amount of dead space between adjacent membranes is similar for bothmembrane types, about 3× the minimum space+2× the minimum line widththat can be patterned and etched, or about 5-10 μm. In a 600 dpi spacingwith a 1 μm minimum line and space 160, that dead space amounts to about25% of the device area. Since filters 22 could be made as small as 20-25μm, or 1000-1200 dpi, the dead space 160 may be a much larger percentageof the device area. The effect of this dead space in conventionalsystems is what's known as the “screen door effect,” a dark gridsuperimposed on the image that is objectionable, particularly whenviewed from close up. However, the main benefit of shrinking the deviceis in lowering of the cost, or increasing the total number of pixels.

As illustrated in FIG. 8, the effect can be minimized in the image byattaching a lens array 26 that broadens the light from each pixel sothat it fills its allocated space on the projected image.

In alternative embodiments, the filters 22 may also be arranged in othergeometrical shapes, such as a triangle, a diamond, a hexagon, atrapezoid, or a parallelogram. The array 20 may be subdivided intoblocks, each with a separate substrate, which may form block of cavities130. A plurality of the blocks may be used in an array to form a largerdisplay system.

In various exemplary embodiments, the filters 22 each may include asilicon membrane attached directly to a silicon spring 134, so that thesilicon membrane may move to change the size of the cavity. In variousother exemplary embodiments, the filters may include membranes asparallel plates attached to a silicon frame. The filters 20 may belocated close to each other without much wasted space in between, sothat the amount of “dead space” between adjacent membranes may bereduced or even minimized, and the space used for display may beincreased or even maximized.

In one embodiment, the microlenses 29 of lens system 26 serve toconverge portions of the image received from adjacent filters 22 tominimize the dead space, as illustrated in FIG. 8.

With reference once more to FIG. 1, the illustrated Fabry-Perot array 20is controlled by the modulator 15. The modulator 15 may be connected tothe Fabry-Perot array 20, and may include a gap control circuit thatcontrols the movement of the mirrors in each cavity. Based on imagemodulation data, each filter 22 is controlled to have a desired cavitysize to allow transmission of a particular wavelength band or collectivewavelength band. The particular or collective wavelength bandcorresponds to the color of a respective image pixel.

The Fabry-Perot filters may also be controlled to provide multiple graylevels (brightness levels) for each color-separated image pixel. Forexample, the cavity may be controlled through time-division multiplexingof the transmitted light to provide multiple gray levels for eachcolor-separated image pixel. The Fabry-Perot filter is one which can beadjusted such that any electromagnetic radiation which is transmitted isoutside the bandwidth of the perceptual limit of human eyes (the“visible range”), generally 400-700 nm. By shifting between a state inwhich the Fabry-Perot filter transmits in the visible range and one inwhich any radiation transmitted is outside the visible range, differentgray levels can be achieved. A pixel is fully “on” when all pre-selectedtransmission wavelengths are swept within the visible range. Thebandwidth is typically less than 60 milliseconds. The pixel is fully“off” when no light in the visible range is transmitted. Transmissionthat is between these two limits creates gray-scale levels.

To limit the amount of light contributing to an image pixel, unwantedlight may be moved into a non-visible part of the spectrum, such asultraviolet or infrared. Alternatively, unwanted light may be completelyblocked by properly adjusting the size of the cavity. For example, todisplay a wavelength of light at half brightness, the membrane may spendhalf of its time set to the gap (size of the cavity) for thatwavelength, and the other half at a gap that does not have constructiveinterference anywhere in the visible spectrum.

In time-division multiplexing, the time resolution of a drivingcircuitry, such as the modulator 15 or a circuitry used in connectionwith the modulator, sets a limit to the number of gray levels(brightness levels) possible for a wavelength. For example, if T is thetime limit of human eyes perceptual time bandwidth to response tochanges in color and i represents the tunable discrete peak wavelengthsfor the transmission spectra available in the Fabry-Perot tunablefilter, then, for a transmission mode display, the gray levels may berepresented by the following integral equation:

$\begin{matrix}{{g_{i}(t)} = \frac{\int_{0}^{t}{\int_{\lambda_{\min}}^{\lambda_{\max}}{{S_{i}(\lambda)}{\mathbb{d}\lambda}{\mathbb{d}t}}}}{g_{{i\_}100}}} & (1)\end{matrix}$

where S_(i) (λ) represents the transmission spectra of the Fabry-Perotfilter for a discrete peak wavelength setting represented by index i,

λ_(min) and λ_(max) are minimum and maximum wavelengths in the visiblerange of the light spectra or any suitable range required forintegrating the transmission wavelengths,

g_(i) _(—) ₁₀₀ represents the maximum gray level for channel index iused to normalize the gray level g_(i)(t).

When there are N number of gray levels required for the displayapparatus (N is typically 256 for a display system) and under timedivision multiplexing, the total time over which the channel i is left“on” satisfies the following condition:

$\begin{matrix}{T \leq {\sum\limits_{i = 1}^{N}T_{i}}} & (2)\end{matrix}$

Modified versions of Equations (1) and (2) may be used to createmultiple gray levels for transmission-type displays. The gray levels forM number of channels may be expressed as:g _(i)(j)=T _(j) V _(i) for i=1,2,3, . . . , M and j=1,2, . . . , N  (3)where V_(i) may be obtained, based on Equation (1), from:

$\begin{matrix}{V_{i} = \frac{\int_{\lambda_{\min}}^{\lambda_{\max}}{{S_{i}(\lambda)}{\mathbb{d}\lambda}}}{g_{{i\_}100}}} & (4)\end{matrix}$Equations (3) and (4) provide gray levels for the display apparatus.

As shown in FIG. 1, light from the source 16 passes through theFabry-Perot array 20. Modulated light is produced by the Fabry-Perotarray and is directed onto the screen for viewing. The modulated lightmay include an image. Each pixel of the modulated image corresponds toone (or more) filters 22 in the array 20. The color of the pixel iscontrolled by the size 132 of the cavity. The brightness of the pixel iscontrolled by time-division multiplexing of the cavity. Thus, an arrayof cavities 130 may correspond to an array of pixels, and thus maycorrespond to an image having the array of pixels. However, it is to beappreciated that two or more filters 22 may correspond to a pixel of theimage.

The image data modulator 30 converts the image data received from theimage source into modulation data for generating an image. The imagedata may include color values, such as L*a*b* values or RGB values foreach pixel of an image. The modulation data may include control signalsfor changing voltages applied to the electrodes of a filter which resultin a cavity distance 132 that provides a desired wavelength band forrendering alone or in combination the desired color values, and timedivision signals for controlling the proportion of the time that afilter 22 spends outside the visible range for achieving selectedbrightness values. The wavelength modulator 32 provides control signalsto control the size of a cavity at a particular time. The brightnessmodulator 34 provides control signals to control the time-divisionmultiplexing of a filter 22. The generated modulated image may betemporarily stored in memory 36 prior to being displayed by theFabry-Perot display apparatus 10.

The modulated image may be one of a series of images modulated from thewhite light passing through the array 20. The series of images may beanimated, such as in a video or a movie. The series of images may alsorepresent stationary images, such as a viewgraph or a page of textualcontent.

In particular, when the light passes through the array 20, enough colorsweeps may be obtained from the array in a spectral space that cover arange of colors required for the pixels by corresponding adjustment ofthe Fabry-Perot cavity size using modulating data from the wavelengthmodulator 32. The color sweeps may be carried out at a high frequency,such as 20 Hz (twenty complete cycles from one bandwidth to the otherand back again) or greater, so that human eyes are not able todistinguish between filtered color coming out of the discrete gapsetting. In one embodiment the filter is shifted between bandwidths at afrequency of 60 Hz or greater (equivalent to about 15-20 ms). Thus, thedisplay apparatus 10 may display color images in various wavelengths bytransmitting selectively very narrow wavelengths or collectively a groupof wavelengths for each image pixel. Similarly, for time divisionmultiplexing, the brightness modulator 34 may shift between bandwidths,only in this case the second bandwidth is outside the visible range.

In FIG. 4, the Fabry-Perot array may include a two-dimensional array ofthin membranes and may be a matrix addressable as a group, orindependently, depending on the application. In the matrix addressableas a group, more than one Fabry-Perot cavity will be actuated togetherto transmit the same wavelengths. Addressing a group or single cavityindependently allows different wavelengths to pass through the filter atthe same time. The actuation of the addressing may be performed by themodulator 15, by modulating the voltage signals provided to drive thecavities 130.

FIG. 9 outlines an exemplary process for controlling a displayapparatus. It is understood that the order of steps need not necessarilybe as shown in FIG. 9 and that one or more of the steps in FIG. 9 may beomitted or that different steps may be provided. As shown in FIG. 9, theprocess starts at step S500 and proceeds to step S510, where light froman illuminator is received at the display apparatus 10. Next, at stepS512, image data is received. At step S514, the data is converted tomodulation signals which include wavelength information and brightnessinformation. At step S516 an array of the display apparatus iscontrolled to generate an array of respective pixels of an image basedon the modulation signals. Then, in step S518, the generated image isdisplayed on the screen. The process ends at step S520.

The method illustrated in FIG. 9 may be implemented in a computerprogram product that may be executed on a computer. The computer programproduct may be a computer-readable recording medium on which a controlprogram is recorded, or may be a transmittable carrier wave in which thecontrol program is embodied as a data signal.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

1. A projection system, comprising: a display apparatus comprising aplurality of tunable Fabry-Perot filters, each of the filters beingconfigured for shifting between a state in which the filter transmitsradiation in a bandwidth in the visible range of the electromagneticspectrum and a state in which the filter transmits radiation in abandwidth outside the visible range of the electromagnetic spectrum; anilluminator which provides light to the plurality of Fabry-Perotfilters; a control system which receives image data and controls thedisplay apparatus to project an image onto an associated displaysurface, the control system comprising a modulator which: provideswavelength modulation signals to the plurality of Fabry-Perot filters tomodulate a color of pixels in the image; and causes selected ones of theFabry-Perot filters to shift into the bandwidth outside the visiblerange to modulate the brightness of pixels in the image.
 2. Theprojection system of claim 1, wherein the display apparatus furthercomprises a projection lens system for magnifying the projected image.3. The projection system of claim 2, wherein the projection lens systemcomprises a plurality of microlenses, the projection lens systemconverging portions of the image received from adjacent filters.
 4. Theprojection system of claim 1, further comprising: a screen onto whichthe image is projected by the display apparatus.
 5. The projectionsystem of claim 4, wherein the screen is remote from the displayapparatus.
 6. The projection system of claim 5, wherein the screen isreflective.
 7. The projection system of claim 1, wherein the modulatorcauses selected ones of the Fabry-Perot filters to shift between abandwidth in the visible range and a bandwidth outside the visible rangeat a frequency at which the two bandwidths are not separately detectableby the eye.
 8. The projection system of claim 1, wherein the brightnessmodulator causes selected ones of the Fabry-Perot filters to shiftbetween a bandwidth in the visible range and a bandwidth outside thevisible range at a frequency of at least 20 Hz.
 9. The projection systemof claim 8, wherein the frequency is at least 60 Hz.
 10. The projectionsystem of claim 1, wherein the brightness modulator causes selected onesof the Fabry-Perot filters to shift between bandwidths usingtime-division multiplexing.
 11. The projection system of claim 1,wherein the display apparatus further comprising a lens intermediate theilluminator and the Fabry-Perot filters.
 12. The projection system ofclaim 1, wherein each of the Fabry-Perot filters is capable ofselectively transmitting radiation in any one of a plurality ofbandwidths in the visible range of the electromagnetic spectrum.
 13. Theprojection system of claim 1, wherein the each of the Fabry-Perotfilters comprises a pair of mirrors, and the control system adjusts adistance between the pair of mirrors based on the image data.
 14. Theprojection system of claim 13, wherein the mirrors are supported on atransparent substrate.
 15. The projection system of claim 1, wherein thefilters are arranged in an array.
 16. The projection system of claim 1,wherein each of the filters is individually addressable.
 17. A method ofprojecting an image with the projection system of claim 1, comprising:receiving image data for an image to be projected; illuminating aplurality of the tunable Fabry-Perot filters; and controlling thetunable Fabry-Perot filters to project the image onto an associateddisplay surface including providing wavelength modulation signals to theplurality of Fabry-Perot filters to modulate a color of pixels in theimage and causing selected ones of the Fabry-Perot filters to shift intothe bandwidth outside the visible range to modulate the brightness ofpixels in the image in accordance with the image data.
 18. The method ofclaim 17, wherein the causing of causing of selected ones of theFabry-Perot filters to shift into the bandwidth outside the visiblerange includes causing selected ones of the Fabry-Perot filters to shiftbetween a bandwidth in the visible range and a bandwidth outside thevisible range at a frequency of at least 20 Hz.
 19. The method of claim17, wherein the frequency is at least 60 Hz.
 20. The method of claim 17,further comprising diverging the image with a lens array comprising aplurality of microlenses.
 21. A computer program product includingcomputer-Executable instructions for performing the method of claim 17.22. A projection system comprising: an image source which supplies imagedata for an image to be projected; an array of individually tunableFabry-Perot filters mounted on a common transparent substrate, each ofthe filters being configured for transmitting visible lighttherethrough; an illuminator which provides light to the plurality ofFabry-Perot filters; a control system which receives image data andcontrols the display apparatus to project an image onto an associateddisplay surface, the control system comprising a modulator whichprovides wavelength modulation signals to the plurality of Fabry-Perotfilters to modulate a color of pixels in the image; and a lens systemwhich includes an array of microlenses intermediate the array of filtersand the associated display surface.